JPH10341135A - Surface acoustic wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small size, low loss surface acoustic wave device without using a transmission line for impedance matching, where deterioration of the VSWR in a pass band is hardly caused and which converts more than one frequency bands. SOLUTION: A 1st SAW filter whose pass band is set to a relatively high frequency region is connected to an input terminal IN1 and a 2nd SAW filter whose pass band is set to a relatively low frequency region is connected to an input terminal IN2 ; output sides of the 1st and 2nd SAW filters 22, 23 are connected at a connecting point 24, which leads to an output terminal OUT; 1st 1-terminal pair SAW resonators 26, 27 are connected between the 1st SAW filter 22 and the connecting point 24 so that the anti-resonance frequency is set to a higher frequency than the pass band of the 1st SAW filter 22; and 2nd 1-terminal pair SAW resonators 25 are connected between the 1st SAW filter 23 and the connecting point 24 so that the anti-resonance frequency is set to a higher frequency than the pass band of the 1st SAW filter 23.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device formed by combining a plurality of SAW filters, and more particularly, it can be used as a filter having two or more passbands, such as a mobile communication device. The present invention relates to a surface acoustic wave device that can be suitably used in a personal computer.

[0002]

2. Description of the Related Art In recent years, mobile communication devices have become more sophisticated, and for example, multi-band compatible mobile phones having two or more communication systems are being studied. To realize such a mobile phone, a broadband bandpass filter that can cover two or more bands is required. However, it has been difficult to realize a low-loss and wide-band filter that can cover two or more bands with a single element.

[0003] Attempts have been made to construct a filter device that can cover two or more bands by combining a plurality of bandpass filters into one component.

For example, Japanese Patent Application Laid-Open No. 7-66679 discloses a duplexer obtained by combining a plurality of bandpass filters. FIG. 1 schematically shows the configuration of the duplexer disclosed in the prior art.

That is, a first band-pass filter 2 having a relatively high pass band in the input terminals IN ₁ and IN ₂ and a _second band-pass filter having a relatively low pass band in the frequency region. The filters 3 are connected to each other. Output terminals of the first and second bandpass filters 2 and 3 are connected at a connection point 4. Note that the first and second
At least the second band-pass filter 3 of the band-pass filters 2 and 3 is composed of a SAW filter.

Here, at least one one-port SAW resonator 5 is connected in series to the second band-pass filter 3. The anti-resonance frequency of the one-port SAW resonator 5 is
Within the passband of the first bandpass filter 2 or
It is located between the passbands of the second bandpass filters 2 and 3. That is, by using the one-port SAW resonator 5, the second bandpass filter whose passband is in a relatively low frequency region among the first and second bandpass filters 2 and 3 having different passbands. It is said that the amount of attenuation on the high frequency side of No. 3 is increased. Further, it is stated that an external circuit for impedance matching on the second bandpass filter 3 side can be simplified. Therefore, it is only necessary to provide the impedance matching transmission line 6 on the first bandpass filter 2 side, and it is not necessary to form a large transmission line for impedance matching on the second bandpass filter 3 side.

[0007]

In the duplexer described in the above prior art, when a transmission line 6 for impedance matching is connected to the first bandpass filter 2, a transmission line having a desired electric length is connected. A relatively large space is required for formation. Therefore, there is a problem that the size of the entire duplexer becomes large.

Further, in order to reduce the size and increase the functionality, SA
When the configuration described in the above prior art is incorporated in the W device package, the width of the transmission line 6 needs to be extremely narrow to obtain a desired characteristic impedance. as a result,
There is a possibility that the insertion loss is deteriorated due to the resistance loss corresponding to the line length. In addition, there is a problem that the area or height of the package is increased, which also increases the cost.

An object of the present invention is to provide a surface acoustic wave device which can solve the above-mentioned drawbacks of the prior art and can cover two or more bands by combining two or more bandpass filters. It is another object of the present invention to provide a small and low-loss surface acoustic wave device that does not require the use of a transmission line for impedance matching, and that is inexpensive.

[0010]

Although not yet known, Japanese Patent Application No. 8-58036 discloses a technique in which the input or output of two SAW filters having different passband frequency characteristics is connected at a connection point, By providing a one-port SAW resonator and a capacitor as means for increasing the impedance of the counterpart SAW filter between the SAW filter in the high frequency range and the connection point,
A surface acoustic wave device has been proposed in which insertion loss is reduced and an impedance matching transmission line is omitted. This configuration will be described with reference to FIG.

In the surface acoustic wave device 11, the first SAW filter 12 whose pass band is in a relatively high frequency region is used.
And a second S whose passband is in a relatively low frequency region.
An AW filter 13 is used. First and second S
The AW filters 12 and 13 are connected at a connection point 14 on the output side. IN ₁ and IN ₂ are input terminals, and OUT 1
Indicates an output terminal. Therefore, the first and second SAW filters 12 and 13 are connected to the connection point 14 on the output end side and the input end IN
₁ and IN ₂ are connected in parallel. here,
One-port SAW resonators 15 and 16 are connected in series between the first and second SAW filters 12 and 13 and the connection point 14, respectively. Further, a capacitor 17 is connected in series between the one-port SAW resonator 15 and the connection point 14.

The one-port SAW resonator 15 and the capacitor 17 are provided at the output terminal of the first SAW filter 12 as means for increasing the impedance of the other filter, that is, the second SAW filter 13. The first and second SAW filters 12 and 13 are formed by the one-port SAW resonator 15 and the capacitor 17.
Of the first SAW filter 1 is suppressed.
In No. 2, the amount of attenuation on the higher frequency side than the pass band is increased. Further, the first and second S
AW filters 12, 13, one-port SAW resonator 15,
It is said that by forming the capacitor 16 and the capacitor 17 on a single piezoelectric substrate, miniaturization and cost reduction can be promoted.

However, when the capacitor 17 is formed on a piezoelectric substrate by, for example, an interdigital electrode structure, a large area is required to obtain a sufficient capacitance for performing the above-described operation, and the size of the piezoelectric substrate is large. Had to be bigger. In addition, since the capacitor 17 must be configured so as not to affect other SAW filters 13 on the same piezoelectric substrate, there is a problem that the arrangement of each element on the chip becomes complicated. Therefore, although it is not necessary to use a transmission line for impedance matching, there is still a limit in reducing the chip size of the surface acoustic wave device.

Further, when the capacitance of the capacitor 17 is reduced in order to further reduce the deterioration of the loss of the other SAW filter, that is, the second SAW filter 13, the VSWR in the pass band deteriorates. There was also.

In view of the above-mentioned problems of the surface acoustic wave device which is not yet known, the present inventor can make the device more compact, have a lower loss, and have a VSW in the pass band.
As a result of intensive studies on a surface acoustic wave device in which characteristics such as R are unlikely to deteriorate, the present invention has been achieved.

That is, the first aspect of the present invention is a surface acoustic wave device comprising a plurality of SAW filters connected to each other, wherein the first SA having a pass band in a relatively high frequency region.
An AW filter, and a second SAW filter having a pass band in a relatively low frequency region, wherein the first and second SAW filters are provided.
One end of the W filter is a first or second input terminal or an output terminal, and the other end of the first or second SAW filter is connected at a connection point and is an output terminal or an input terminal. At least one of the first SAW filters, which are connected in series between the first SAW filter and the connection point, and whose anti-resonance frequency is higher than a pass band of the first SAW filter. One one-port SAW resonator is connected in series between the second SAW filter and the connection point, and the anti-resonance frequency is higher than the pass band of the second SAW filter. And at least one second one-port SAW resonator configured as described above.

According to a second aspect of the present invention, at least one of the first one-port SAW resonator and the second one-port SAW resonator has a multi-stage structure, and the plurality of one-port SAW resonators has a plurality of stages. At least one terminal pair SAW of the SAW resonator
The wavelength of the interdigital transducer of the resonator is
The remaining one-port pair SA of the plurality of one-port SAW resonators
The wavelength is different from the wavelength of the interdigital transducer of the W resonator.

According to the third aspect of the invention, at least one of the first one-port SAW resonator and the second one-port SAW resonator has a multi-stage structure, and Of the terminal pair SAW resonators, the number of electrode fingers of the reflector of at least one one port pair SAW resonator is the same as that of the remaining one terminal pair of the plurality of stages of one port pair SAW resonators. The number of electrode fingers is different.

Preferably, the first and second SAW filters and the first and second one-port SAs are provided.
The W resonators are configured on the same piezoelectric substrate, thereby further reducing the size.

According to a fifth aspect of the present invention, there is provided a communication device using the surface acoustic wave device according to the present invention, wherein a first port connected to an antenna is provided at one end, and a transmitter or a transmitter is provided at the other end. A surface acoustic wave device provided with second and third ports connected to a receiver, and second and third ports of the surface acoustic wave device.
And a transmission or reception circuit connected to the first port, wherein the surface acoustic wave device is connected between the first and second ports, and the first or second port has a passband in a relatively high frequency region.
And a second SAW filter connected between the first and third ports and having a pass band in a relatively low frequency range, and a second port between the first port and the second port. , At least one first terminal connected in series to the first SAW filter and configured to have an anti-resonance frequency higher than a pass band of the first SAW filter. An anti-SAW resonator;
The second S between a first port and a third port;
At least one second one-port SAW resonator connected in series to the AW filter and configured to have an anti-resonance frequency higher than a pass band of the second SAW filter. A communication device characterized in that:

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A non-limiting embodiment of a surface acoustic wave device according to the present invention will be described below with reference to the drawings.

FIG. 3 is a diagram showing a circuit configuration of a surface acoustic wave device according to one embodiment of the present invention. Surface acoustic wave device 21
Has a configuration in which a first SAW filter 22 and a second SAW filter 23 having different pass bands are connected at a connection point 24 on the output side. That is, the input terminal IN _1,
Relatively passband are first SAW filter 22 is connected in the high frequency range, a second SAW filter relatively passband to the input terminal IN ₂ is in the low frequency range 2
3 are connected.

FIG. 17 is a schematic plan view showing a specific configuration of a surface acoustic wave device according to one embodiment of the present invention. FIG. 18 is a diagram showing the surface acoustic wave device housed in a package. It is sectional drawing which shows a structure.

As is apparent from FIG. 17, the surface acoustic wave device 21 is configured using a rectangular piezoelectric substrate 31. The piezoelectric substrate 31 is made of piezoelectric ceramics such as lead zirconate titanate-based ceramics, quartz, or LiTa.
It can be made of a piezoelectric single crystal such as O ₃ and LiNbO _{3. In} this embodiment, 36 ° YX LiTaO ₃
It is composed of a substrate.

On the piezoelectric substrate 31, input terminals IN ₁ , I
N ₂ is formed by forming a conductive film. The input terminal IN _1, the first SAW filter 22 are connected. The SAW filter 22 includes three IDTs 22a.
~ 22c. Is one of the comb electrodes of the central IDT22b is connected to the input terminal IN _1, the other comb electrode is grounded. One of the IDTs 22 a and 22 c is grounded, and the other IDT is connected to the connection point 32. IDT22a-22
Reflectors 22d and 22e are formed on both sides of the region where c is provided in the surface wave propagation direction.

On the other hand, the input terminal IN ₂ has a second SAW
Filter 23 is connected. The second SAW filter 23 has three IDTs 23a to 23c. One comb electrode of the central IDT 23b is grounded, and the other comb electrode is connected to a SAW resonator 25 described later. IDTs 23a, one of the comb electrodes of 23c are is grounded, and the other comb electrode is connected to the connection point 33, the connection point 33 is connected to the input terminal IN _2.

Reflectors 23d and 23e are formed on both sides of the region where the IDTs 23a to 23c are provided in the surface wave propagation direction. One-port SAW resonators 26 and 27 are connected in series between the connection points 32 and 24. The one-port SAW resonator 26 includes an IDT 26a,
Reflectors 26b and 26c arranged on both sides of the IDT 26a in the direction of propagation of the surface acoustic wave. One-port SAW resonator 27
Similarly, the IDT 27a located at the center
And reflectors 27b and 27c arranged on both sides. One end of the one-port SAW resonator 27 is connected to the connection point 24.

A one-port SAW resonator 25 is connected between one comb-shaped electrode of the IDT 23 b at the center of the second SAW filter 23 and the connection point 24. The one-port SAW resonator 25 includes an IDT 25 disposed at the center.
a, and reflectors 25b and 25c arranged on both sides thereof.

The connection point 24 is connected to the output terminal OUT. First and second SAW filters 22 and 23 formed on piezoelectric substrate 31, one-port SAW resonator 25
To 27, input terminals IN ₁ and IN ₂ and output terminal OUT
Are formed on the piezoelectric substrate 31 by patterning a conductive material such as Al.

As described above, by configuring each element of the above-described embodiment on a single piezoelectric substrate 31, it is possible to easily reduce the size of the surface acoustic wave device 21 having a plurality of pass bands. . In addition, since the electrodes can be simultaneously formed by patterning a conductive material such as Al on the piezoelectric substrate 31, the manufacturing process does not become complicated.

The surface acoustic wave device 21 is, for example, shown in FIG.
As shown in (1), it can be built in a package like a normal surface acoustic wave filter. That is, in the surface acoustic wave device 34 shown in FIG. 18, the surface acoustic wave device 21 is housed in a package 35 made of insulating ceramics. The package 35 includes a rectangular frame member 35b, 3 on a ceramic substrate 35a made of insulating ceramics.
5c is provided. The surface acoustic wave device 2 is placed in the opening 35e of the package body 35d.
1 are arranged and fixed to the ceramic substrate 35a. The input terminals and output terminals of the surface acoustic wave device 21 and the electrodes connected to the ground potential (electrodes indicated by hatching in FIG. 17) are appropriately connected to the package body 35d by bonding wires 36a and 36b. It is electrically connected to the formed electrode for connection with the outside. The opening 35e is closed by a cover 37 made of metal.

As is clear from FIG. 18, the surface acoustic wave device 21 of the present embodiment is different from a normal surface acoustic wave device by using a package 35 for packaging a conventionally used surface acoustic wave device. Similarly, it can be provided as a package built-in type electronic component.

The pass band of the first SAW filter 22 is
870 to 885 MHz, and FIG. 4 shows frequency amplitude characteristics inside and outside the pass band of the first SAW filter 22. FIGS. 5A and 5B show the first SAW filter 2.
2 shows an impedance Smith chart on the input side and the output side on the output side, respectively.

The second SAW filter 23 has a pass band of 810 to 828 MHz, and FIG.
9 shows frequency amplitude characteristics inside and outside the pass band of the filter 23.
FIGS. 7A and 7B are diagrams showing impedance Smith charts on the input side and the output side of the second SAW filter 23, respectively.

Referring back to FIG. 3, the first SAW filter 22
And a connection point 24, a plurality of stages of one-port SAW resonators, that is, first one-port SAW resonators 26 and 27
Are connected in series. Here, the one-port SAW resonators 26 and 27 are connected in series to the first SAW filter 22 such that the anti-resonance frequency is located on the higher frequency side than the pass band of the first SAW filter 22. Have been.

The one-port SAW resonator 26 and the one-port SAW resonator 27 have the same configuration, and FIG. 8 shows the frequency amplitude characteristics of the one-port SAW resonator 26 as a representative. .

FIGS. 9A and 9B show the first S
On the output side of the AW filter 22, the two-stage one-port pair SA is provided.
In the configuration in which the W resonators 26 and 27 are connected in series,
It is a figure showing an impedance Smith chart inside and outside a pass band in an input terminal and an output terminal.

FIGS. 5B and 9 show output-side impedance Smith charts of the first SAW filter 22 itself.
9B, one terminal pair SA is shown in FIG.
By connecting the W resonators 26 and 27, 810 to 8
It can be seen that the impedance at 28 MHz is high.

FIG. 10 shows the first SA as shown in FIG.
The first embodiment in the present embodiment to which the W filter 22 is connected
3 shows the frequency amplitude characteristics inside and outside the pass band and the VSWR on the SAW filter 22 side. Here, a 10 nH impedance matching inductance element 28 is connected between the connection point 24 and the ground potential. Also, the second
The input side of the SAW filter 23 is terminated with 50Ω.

The frequency amplitude characteristic indicated by the broken line is a characteristic enlarged on the scale shown on the right side of the vertical axis. Similarly, in FIGS. 12 to 16, the broken line indicates the expanded frequency amplitude characteristic. And

On the other hand, FIGS. 11A and 11B show one-port SAW resonators 15 connected in series to the output side of the first SAW filter 12 as shown in FIG.
When the capacitor 17 of F is connected in series,
4 shows an impedance Smith chart inside and outside a pass band on the input side and the output side. Here, one-port SAW resonator 15
The one having the same characteristics as the one-port SAW resonator 26 is used.

In FIG. 11B, 810 is connected by connecting the one-port SAW resonator 15 and the capacitor 17.
FIG. 9 (b)
It can be seen that it is higher as in the case of the impedance Smith chart shown in FIG. However, FIG.
In the impedance Smith chart shown in FIG. 9B, in the impedance in the pass band, the deviation of the impedance from 50Ω pure resistance to capacitive is larger than that in the impedance Smith chart shown in FIG. Recognize.

FIG. 12 shows frequency amplitude characteristics inside and outside the pass band on the first SAW filter 12 side in the conventional circuit configuration shown in FIG. Here, the parallel connection point 14
A 10 nH impedance matching inductance element 18 is connected between the
The input side of the SAW filter 13 is terminated with 50Ω.

FIG. 12 is compared with FIG. 10. In the surface acoustic wave device of this embodiment shown in FIG. 10, only the one-port SAW resonator is used. In comparison, it can be seen that the insertion loss can be suppressed to the same level or less. V in the pass band
Regarding the SWR, the surface acoustic wave device of the present embodiment shown in FIG. 10 is smaller than the conventional example shown in FIG.
It can be seen that the difference is 0.5. Further, in the frequency amplitude characteristic of the surface acoustic wave device of the present embodiment shown in FIG. 10, the attenuation on the high frequency side in the pass band is also shown in FIG.
It can be seen that it is about 3 dB larger than the case of the conventional example shown in FIG.

FIG. 13 shows frequency amplitude characteristics inside and outside the pass band of the second SAW filter 23 in the surface acoustic wave device configured as shown in FIG. Here, a 10 nH impedance matching inductance element 28 is connected between the parallel connection point 24 and the ground potential, and the input side of the first SAW filter 22 is terminated with 50Ω.

FIG. 13 shows that the one-port SAW resonator 26,
27, the output 81 of the first SAW filter 22 is used.
It can be seen that by increasing the impedance at 0 to 828 MHz, good passband characteristics and good attenuation characteristics are also obtained on the second SAW filter 23 side.

On the other hand, FIG. 14 shows the frequency amplitude characteristics inside and outside the pass band on the first SAW filter side when connected according to the circuit diagram of the embodiment shown in FIG. Of the SAW resonators 26 and 27, the wavelength of the IDT of one SAW resonator is made different from the wavelength of the IDT of the SAW resonator, and the frequency is increased by 2.5 MHz. A 10 nH impedance matching inductance element 28 is connected between the parallel connection point 24 and the ground potential, and the input side of the second SAW filter 23 is terminated with 50Ω.

A comparison between FIG. 14 and FIG. 10 shows that in FIG. 14, the ripple in the pass band is reduced. That is, in the one-port SAW resonator, a ripple occurs in the pass band of the first SAW filter 22 due to the influence of the reflectors provided on both sides of the IDT. Therefore,
When the one-port SAW resonators 26 and 27 having the same characteristics are connected in series to form a two-stage configuration, the ripple appears more strongly. Therefore, in the modification shown in FIG. 14, the ripples in the pass band are offset by making the frequencies of the one-port SAW resonator 26 and the one-port SAW resonator 27 different, and as a result, The ripple in the pass band is reduced. In this modification, one terminal pair SA
The wavelengths of the IDTs in the W resonators 26 and 27 are different, but instead or in addition, the number of the electrode fingers of the reflector of the one-port SAW resonator 26 is changed to the one-port SAW resonator. The number of electrode fingers of the twenty-seventh reflector may be different, and the ripple in the pass band can be similarly reduced.

FIG. 15 shows frequency amplitude characteristics inside and outside the pass band of the surface acoustic wave device prepared for comparison. This surface acoustic wave device has a configuration in which the output terminal of the first SAW filter 22 and the output terminal of the second SAW filter 23 are directly connected. FIG. 15 shows the configuration of the first SAW filter 22 in this case. 7 shows frequency amplitude characteristics inside and outside the pass band on the side. Here, a 10 nH impedance matching inductance element is connected between the connection point of the first and second SAW filters and the ground, and the second SAW filter is connected to the ground.
The input side of the W filter 23 is terminated with 50Ω.

As is apparent from a comparison between FIGS. 10, 14 and 15, the frequency amplitude characteristic shown in FIG.
Although the deterioration of the loss in the SAW filter is small,
It can be seen that the VSWR in the pass band increases and the attenuation on the high frequency side of the pass band decreases.

FIG. 16 shows the frequency amplitude characteristics inside and outside the pass band on the second SAW filter side of the surface acoustic wave device prepared for comparison having the characteristics shown in FIG.
Here, an impedance matching inductance element of 10 nH is connected between the parallel connection point and the ground potential, and the input side of the first SAW filter 22 is 50Ω.
Terminated with

As is apparent from a comparison between FIG. 13 and FIG. 16, FIG. 16 shows that the insertion loss in the second SAW filter 23 is large. FIG. 19 is a circuit diagram illustrating an example of a communication device configured using the surface acoustic wave device according to the present invention.

The communication device 41 of the present embodiment includes the surface acoustic wave device 21 and transmission or reception circuits 45 and 46. The surface acoustic wave device 21 has a first port 21A connected to the antenna 42. Port 21A is
Configure the input or output end. Further, the surface acoustic wave device 21 includes second and third ports 21B and 21C.
The second and third ports 21B and 21C constitute an output terminal or an input terminal.

In the surface acoustic wave device 21, similarly to the surface acoustic wave device of the embodiment shown in FIG. 3, a first SAW filter 22 and a second SAW filter 23 having different pass bands are formed. ing.

The first SAW filter 22 is in a frequency range where the pass band is relatively high, and the second SAW filter 23 is in a frequency range where the pass band is relatively low. The first SAW filter 22 is connected between the above-described first port 21A and second port 21B. In addition, in series with the first SAW filter 22, at least one, in this embodiment, two first one-terminal pairs SA
W resonators 26 and 27 are connected in series. The one-port SAW resonators 26 and 27 have an anti-resonance frequency of the first
Is configured to be on the higher frequency side than the pass band of the SAW filter 22.

On the other hand, the second SAW filter 23 is connected between the first port 21A and the third port 21C, and a second terminal is connected in series with the second SAW filter 23. The SAW resonator 25 is connected. The second one-port SAW resonator 25 is configured so that its anti-resonance frequency is higher than the pass band of the second SAW filter 23. Further, a plurality of second one-port SAW resonators 25 may be connected in series.

Therefore, this surface acoustic wave device 21 is
Since the configuration is almost the same as that of the surface acoustic wave device shown in FIG. 3, the specific configuration and operation of the surface acoustic wave device 21 will be omitted by referring to the description made with reference to FIG.

In the communication device of this embodiment, the surface acoustic wave device 2
One first port 21 </ b> A is connected to an antenna 42 by an antenna line 43. On the other hand, the second and third ports 21B and 21C are connected to transmission or reception circuits 45 and 4 respectively.
6 is connected. Note that the transmitting or receiving circuit is
This means that any of a transmission circuit and a reception circuit may be used. That is, the second and third ports 21B and 21C
May be connected to the transmission circuits 45 and 46, the reception circuits 45 and 46 may be connected, or the transmission circuit 45 and the reception circuit 46 or the transmission circuit 46 and the reception circuit 45 may be connected to the. Thus, the surface acoustic wave device 21
By using the above, it is possible to easily configure a communication device that is small in size and utilizes the advantages of the surface acoustic wave device 21.

[0059]

In the surface acoustic wave device according to the first aspect of the present invention, one ends of the first and second SAW filters having different pass bands are used as the first and second input terminals or output terminals, respectively. In the configuration in which the other end is connected at a connection point to be an output terminal or an input terminal, an anti-resonance frequency between the first SAW filter and the connection point is set to the first SAW filter.
At least one first one-port SAW resonator is connected so as to be on the higher frequency side than the pass band of the filter, and the anti-resonance frequency is between the second SAW filter and the connection point. Since at least one second one-port SAW resonator is connected in series so as to be on a higher frequency side than the pass band of the second SAW filter, the first one-port SAW resonator provides The impedance of the first SAW filter in the pass band of the second SAW filter is increased, and the first one-port SAW resonator provides the first SAW filter.
, The impedance of the second SAW filter in the pass band of the SAW filter is increased. Therefore, while suppressing the deterioration of the insertion loss of the first and second SAW filters, the amount of attenuation on the higher frequency side than the respective passbands is increased.

In addition, the configuration described in the prior art which uses the one-port SAW resonator and the capacitor, which has not been known, has a problem that the size of the piezoelectric substrate is increased by the capacitor component. , One terminal pair S
According to the configuration of the present invention using the AW resonator, it is possible to reduce the insertion loss of the first SAW filter and suppress the deterioration of the VSWR in the pass band without increasing the size of the piezoelectric substrate.

Further, at least one of the first and second one-port SAW resonators has a plurality of stages, and at least one of the first and second one-port SAW resonators has a plurality of stages. When the wavelength of the IDT of one SAW resonator is different from the wavelength of the IDT of another SAW resonator, ripples in the pass band of the first SAW filter are effectively reduced. be able to.

Furthermore, in a configuration having a plurality of stages of one-port SAW resonators, the number of electrode fingers of the reflector of at least one one-port SAW resonator may be changed to another one. Similarly, when the number of electrode fingers of the reflector of the terminal pair SAW resonator is different from the number of electrode fingers, the first and second S
The ripple in the pass band of the AW filter can be effectively reduced.

As described in claim 4, the first and second S
When the AW filter and the first and second one-port SAW resonators are formed on a single piezoelectric substrate, electrodes for forming each element can be easily formed on the piezoelectric substrate 10. The surface acoustic wave device of the present invention can be configured without complicating the steps, and the size and cost of the surface acoustic wave device according to the present invention can be further reduced.

As described in claim 5, by connecting the surface acoustic wave device according to the invention of claim 1 to two transmitting or receiving circuits, a communication device suitable for a diversity type communication device is constituted. can do. In this case, since the surface acoustic wave device according to the present invention is used, the attenuation of the element area in the vicinity of the pass band can be increased,
Therefore, it is possible to configure a communication device having excellent selectivity, and it is possible to configure each SAW filter and one-port SAW resonator on a single piezoelectric substrate. In addition, a communication device having excellent selectivity can be easily configured.

[Brief description of the drawings]

FIG. 1 is a circuit diagram for explaining a conventional surface acoustic wave device in which two bandpass filters having different pass bands are connected.

FIG. 2 is a circuit diagram showing another example of a conventional surface acoustic wave device in which two band pass filters having different pass bands are connected.

FIG. 3 is a circuit diagram of a surface acoustic wave device according to one embodiment of the present invention.

FIG. 4 is a diagram showing a frequency amplitude characteristic of a first SAW filter in the embodiment shown in FIG. 3;

FIGS. 5A and 5B are impedance Smith charts of a terminal including two IDTs outside the first SAW filter and an opposite terminal thereof in the embodiment shown in FIG. 2; FIG.

FIG. 6 is a diagram showing a frequency amplitude characteristic of a second SAW filter in the embodiment shown in FIG. 3;

FIGS. 7A and 7B are impedance Smith charts of terminals on the second SAW filter side including the two outer IDTs and terminals on the opposite side of the second SAW filter in the embodiment shown in FIG. 3; FIG.

FIG. 8 shows a first terminal pair S in the embodiment shown in FIG.
The figure which shows the frequency amplitude characteristic of an AW resonator.

FIGS. 9 (a) and (b) show an input terminal and a two-stage SAW resonator connected in series to a first SAW filter in the embodiment shown in FIG. 3, respectively. The figure which shows the impedance Smith chart in an output terminal.

FIG. 10 is a view showing a frequency amplitude characteristic and a VSWR on the first SAW filter 22 side in the embodiment shown in FIG. 3;

11A and 11B show a case where a one-port SAW resonator is connected to the output side of a first SAW filter and a capacitor is further connected in series in the surface acoustic wave device shown in FIG. 2; The figure which shows the impedance Smith chart inside and outside the pass band of FIG.

FIG. 12 is a diagram showing a frequency amplitude characteristic inside and outside a pass band and a VSWR on the first SAW filter side in the surface acoustic wave device shown in FIG. 2;

FIG. 13 shows a frequency amplitude characteristic and a VSWR of a second SAW filter in the surface acoustic wave device of the embodiment shown in FIG.
FIG.

FIG. 14 is a diagram showing a frequency amplitude characteristic and a VSWR on a first SAW filter side in a modification connected according to the embodiment shown in FIG. 3;

FIG. 15 shows a first example of a surface acoustic wave device prepared for comparison.
Amplitude characteristics and VSW on the SAW filter side of
The figure which shows R.

FIG. 16 shows a second example of the surface acoustic wave device prepared for comparison.
Amplitude characteristics and VSW on the SAW filter side of
The figure which shows R.

FIG. 17 is a schematic plan view for explaining a specific structure example of the surface acoustic wave device according to the embodiment shown in FIG. 3;

18 is a cross-sectional view for explaining a structure in which the surface acoustic wave device shown in FIG. 17 is housed in a package.

FIG. 19 is a circuit diagram illustrating an example of a communication device configured using the surface acoustic wave device according to the present invention.

[Explanation of symbols]

Reference Signs List 21 surface acoustic wave device 21A first port 21B second port 21C third port 22 first SAW filter 23 second SAW filter 25 second one-terminal SAW resonator 26 , 27... First one-port SAW resonator IN ₁ , IN ₂ ... Input terminal OUT... Output terminal 41.

Claims (5)

[Claims] 1. A surface acoustic wave device comprising a plurality of SAW filters connected to each other, the first SAW having a pass band in a relatively high frequency region.
A filter and a second SAW whose passband is in a relatively low frequency range
One end of each of the first and second SAW filters,
A second input terminal or an output terminal; the other ends of the first and second SAW filters are connected at a connection point to be an output terminal or an input terminal; and the first SAW filter and the connection point And at least one first one-port SAW resonator configured such that the anti-resonance frequency is higher than the pass band of the first SAW filter, and At least one of the first SAW filters, which are connected in series between the second SAW filter and the connection point, and whose anti-resonance frequency is higher than a pass band of the second SAW filter. A surface acoustic wave device further comprising two one-port SAW resonators. 2. At least one of the first one-port SAW resonator and the second one-port SAW resonator has a multi-stage configuration, and at least one of the plurality of one-port SAW resonators. The wavelength of the interdigital transducer of one one-port SAW resonator is different from that of the plurality of one-port SAs.
The surface acoustic wave device according to claim 1, wherein the wavelength is different from the wavelength of the interdigital transducer of the remaining one terminal pair of the W resonator and the SAW resonator. 3. At least one of the first one-port SAW resonator and the second one-port SAW resonator has a multi-stage configuration, and the one-port SAW resonator has a multi-stage configuration. The number of electrode fingers of the reflector of at least one one-port SAW resonator is different from the number of electrode fingers of the remaining one-port SAW resonator of the plurality of one-port SAW resonators; The surface acoustic wave device according to claim 1 or 2, wherein: 4. The first and second SAW filters and the first and second SAW filters.
The surface acoustic wave device according to any one of claims 1 to 3, wherein the second one-port SAW resonator is formed on a single piezoelectric substrate. 5. A surface acoustic wave device provided with a first port connected to an antenna on one end side, and second and third ports connected to a transmitter or a receiver on the other end side. A transmission or reception circuit connected to the second and third ports of the surface acoustic wave device, wherein the surface acoustic wave device is connected between the first and second ports, and the pass band is relatively high. A first SAW filter in a relatively high frequency range;
A second SAW filter connected between the first and third ports and having a passband in a relatively low frequency range; and a first SAW filter between the first port and the second port.
At least one of the first SAW filters connected in series and configured to have an anti-resonance frequency higher than the pass band of the first SAW filter.
One port SAW resonator, and the second S between a first port and a third port.
At least one second one-port SAW resonator connected in series to the AW filter and configured to have an anti-resonance frequency higher than a pass band of the second SAW filter. A communication device, characterized in that: